Diamagnetic levitation system

ABSTRACT

The invention concerns an inertial sensor or an actuator based on diamagnetic levitation, said inertial sensor or actuator comprising support means serving as main support body for an inertial sensor or for an actuator, a two dimensional array of permanent magnets and a diamagnetic element facing the said array characterized in that said diamagnetic material constitutes the inertial mass or the moving part of the actuator.

FIELD OF THE INVENTION

The present invention relates to non-contact systems based ondiamagnetic levitation.

BACKGROUND OF THE INVENTION

Current inertial sensing systems such as accelerometers, gravimeters andinclinometers are based on the relative displacement between an inertialmass and the base of the instrument when the said base is subject to anexternal perturbation (vibration, modification of the “g” level, angle);and gyroscopes, which are another kind of inertial sensing system, aremade of an inertial mass which is rotated about one of its axis ofinertia and the measurement principle relies on the relative movementbetween the said axis and the base of the instrument, or on the forcegenerated by the said axis on the base of the instrument, when the saidbase is subject to an external movement.

The limitation of all those inertial sensing systems is mainly due tofriction between the inertial mass and the base of the instrument.

Indeed this friction is responsible of imprecision in the measurement,of wear between the mechanical parts in contact and it might also leadto failure due to mechanical fatigue.

In addition inertial sensing systems, such as seismometers in seismologyor inclinometers in civil engineering, are often placed to monitorstructures or machines and the power consumption of such systems issometimes a critical factor.

Hence there is a need to make non-contact (contact less) inertialsensing systems with little energy consumption.

One way to answer this problem is to use diamagnetic levitation, whichis the only stable passive (no energy input) levitation at roomtemperature:diamagnetic materials are repelled by magnetic fields. Ifthe magnetic field is created by permanent magnets, a piece ofdiamagnetic material can thus be passively and stably levitated.

In the U.S. Pat. No. 3,831,287 a tiltmeter is designed using diamagneticlevitation but without axial contact-less stabilization of thediamagnetic inertial mass. The diamagnetic force exerted over theinertial mass is created by a 1D arrangement of large horseshoe magnetsresulting in an unstable levitation in the axial direction.

In the U.S. Pat. No. 5,396,136 an array of permanent magnets islevitated by magnetic interaction with a diamagnetic material (pyroliticgraphite).

In such a configuration magnets are heavier than graphite for the samevolume of material, and diamagnetic materials (such as pyroliticgraphite) is much more expensive than magnets for the same volume ofmaterial (or for the same weight). In addition such a stabilisation,using a bowl shape diamagnetic material, is not active and would not, ifused as a sensor, behave with the high sensitivity of a force balanceinertial sensing system such as the ones of the present invention.

Other prior art references are listed below:

-   R. Moser, J. Sandtner, H. Bleuler,    Diamagnetic Suspension System for Small Rotors, Journal of    Micromechatronics, Vol. 1, No. 2, 2001.-   R. Moser, J. Sandtner, H. Bleuler, Diamagnetic Suspension Assisted    by Active Electrostatic Actuators, 6^(th) International Symposium on    Magnetic Suspension Technology, Oct. 6^(th) 2001.-   R. Moser, Y-J. Regamey, H. Bleuler, Passive Diamagnetic Levitation    for Flywheels, ISMB, Sep. 24^(th) 2002.-   R. Moser, F. Barrot, H. Bleuler,    Optimization of Two-Dimensionnal Permanent Magnet Arrays for    Diamagnetic Levitation, MAGLEV, Sep. 9^(th) 2002.-   Science Toys, Levitating Pyrolitic Graphite:    http://www.scitoys.com/scitoys/scitoys/magnets/pyrolitic    graphite.html July 2002.

SUMMARY OF THE INVENTION

The present invention relates to a sensor as defined in claim 1 and to abi-directional actuator as defined in claim 11.

Preferred embodiments are defined in the dependent claims.

Advantageously, the present invention combines the use of diamagneticlevitation and electrostatic actuators to create highly sensitivenon-contact inertial sensing systems based on the magnetic levitation ofa diamagnetic body over a two-dimensional permanent magnet array.

In the invention a diamagnetic element is facing a two dimensionalplanar array of permanent magnets

and thus, when the bi-dimensional array of magnets is placedhorizontally, the diamagnetic element floats above the 2D arrangement ofmagnets.

The magnets are arranged in such a way (for instance: oppositepolarities for neighbouring magnets) that the diamagnetic force exertedby the array of magnets overcomes the weight of the diamagnetic element.

Preferably the relative horizontal position between the inertial massand said array of magnets is sensed with one or several non-contactposition sensors; This position information is then used to maintain orto move, with the use of non-contact electrostatic actuators, thediamagnetic element at a precise position above the array of magnets.

To move the diamagnetic element, electrostatic forces are created by atleast 3 electrostatic actuators and the diamagnetic material is part ofan electrode that is common to all said electrostatic actuators. Theother electrode of each electrostatic actuator is made of anon-ferromagnetic material.

As for the said common electrode, if, for instance, we take a discshaped diamagnetic material, the diamagnetic material will be insertedinside a non-ferromagnetic ring shaped metal or a ring shaped electret(that can be pre-charged by electrostatic charges). The association ofthe diamagnetic disc and the ring shaped metal (or ring shaped electret)constitutes the common electrode of the said electrostatic actuators andalso constitutes the inertial mass used in this invention.

Of course the shape of the diamagnetic material and the correspondingnon-ferromagnetic metallic surface (or electret surface) that willtransform the said diamagnetic mass into said common electrode, can befreely chosen.

Of course the invention comprises a mechanical base to hold together thepreviously mentioned components.

In a preferred embodiment the invention comprises a feed-back loopincorporating the electrostatic actuators, the non contact positionsensors, a signal conditioning unit for the sensors, a High voltagepower supply, and a controller which computes the amount of voltage toapply to the independent electrodes of the said electrostatic actuatorsin order to maintain the inertial mass at a predefined position.Moreover the invention may comprise a signal processing unit that can bethe same unit used for the controller or a separate unit.

When a relative movement of the base occurs (due to an acceleration, atilt, etc. . . . ) the controller apply to the electrodes a voltage thatis proportional to the disturbance (acceleration, angle).

It is preferable to measure differentially the position of said inertialmass. This can be done using a unique sensor with several sensing unitor using two identical non-contact position sensors facing two oppositesides of the inertial mass.

In addition, if a disc (or cylindrical) shape diamagnetic element isused with a ring (or cylindrical) shape electret (the electret can bepre-charged), and if each of the three (at least) electrodes facing theelectret is made of, at least, three alternating comb electrodes, then amotor function can be implemented in order to spin the inertial massabout its main inertial axis.

When the relative displacement between the inertial mass and the arrayof magnets is due to an external perturbation (such as a vibration, atilt, a variation in the level of g) then the voltage applied to theelectrostatic actuators in order to keep in place the inertial mass isproportional to the intensity (acceleration, angle) of the appliedperturbation.

Two-dimensional accelerometers (or seismometers), two dimensionaltiltmeters (inclinometer) or gravimeters can be designed on such aconcept.

Hence various small inertial sensing systems made of low cost componentscan be designed on this same basic embodiment (implementation) requiringmainly changes in the signal processing part.

In addition such an invention can also be used as a small X-Y actuatorto move light objects with very small (less than a 1000 micrometer) andprecise displacement (less than 50 nanometer depending on thesensitivity of the non contact distance sensors used). To do so, oneonly needs to give a varying order to the position controller instead ofgiving it a fixed position order.

Besides a feedback loop along a direction Z, orthogonal to the X-Y planof the magnet array, incorporating a Z actuator, as well a Z positionsensor, can be added to the system.

The total absence of contact is the main advantage of the presentinvention since it allows high sensitivity and high accuracymeasurements.

Furthermore, in such an approach, friction problems are overcome withoutspending much energy since the inertial mass is both:

-   -   levitated passively (without energy input) over the base of the        instrument using diamagnetic levitation    -   and maintained at a precise position, adopting the force balance        concept for inertial sensing systems, with the use of        electrostatic actuators.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the nature and objects of the invention,reference should be made to the following detailed description and theaccompanying drawings, in which:

FIG. 1 shows a cut side view of the inertial sensor system with:

-   -   1) Diamagnetic disk    -   2) 2D arrangement of permanents magnets    -   3) Aluminum crown    -   4) Copper electrode    -   5) Optical sensor    -   6) Infrared LED    -   7) Infrared beam passing through a hole in the diamagnetic disc        and a hole in the array of magnets    -   8) Isolating layer    -   9) Structural support    -   10) Magnet with its polarity

FIG. 2 explains the position control of the diamagnetic disc with:

-   -   11) Electrostatic actuator (Copper Electrode+aluminum crown)    -   12) Controller

FIG. 3 shows details of the position control of the diamagnetic disc indifferential mode (for V_(y) the procedure is the same as for V_(x))with:

-   -   13) Electrostatic force exerted on the diamagnetic disc by the        electrostatic actuators    -   14) Voltage amplifier

FIG. 4 explains the signal conditioning of the 4 segments sensor thatcan be used in the inertial sensing system. i_(A), i_(B), i_(C), i_(D)are the currents which are proportionals to the illuminated surface andto the intensity of the spot. With:

-   -   15) Infrared spot

FIG. 5 shows a linear drive made of a diamagnetic material over a 1DHalbach array of magnets with:

-   -   17) Diamagnetic material

FIG. 6 shows diamagnetic material in a 6 degrees of freedom stablelevitation over a 2D Halbach array of permanent magnets.

FIG. 7 shows an unstable contact-less suspension with activeelectrostatic actuators (diamagnetic disc with its aluminum crown andits electrostatic electrodes over a 2D Halbach array of permanentmagnets).

FIG. 8 shows a side view of a diamagnetic material in a 5 degrees offreedom levitation over a 2D Halbach array of permanent magnets, withmagnetic field lines with:

-   -   18) Magnetic field lines

FIG. 9 shows a side view of a diamagnetic material in a three degrees offreedom levitation over a 2D Halbach array of permanent magnets, withmagnetic field lines.

FIG. 10 shows the implementation of the inertial sensor with 2 pairs ofnon contact distance sensors with:

-   -   16) Displacement sensor

FIG. 11 shows a sketch of the electrode used to create a 3 phasesalternating electric field in the gyroscope application with:

-   -   a) Phase 1 electrode    -   b) Phase 2 electrode    -   c) Phase 3 electrode    -   20) Front view of the 3 phases electrode    -   21) Back view of the 3 phases electrode

FIG. 12 shows a top view of an inertial disc shaped mass with twoorthogonal pairs of double electrodes with:

-   -   4′) Inner copper electrode    -   4″) Outer copper electrode

FIG. 13 Possible magnets arrays for diamagnetic levitation, a)Opposite2D b) Opposite 1D, c) Repulsive 2D, d) repulsive 1D, e) Halbach1D f) Halbach 2D g) reference magnet.

DETAILED DESCRIPTION OF THE INVENTION

Several kinds of precision instruments can be designed on the principleof a diamagnetic material levitated over a 2D array of permanent magnetsand kept in a precise position with electrostatic actuation.

We will describe a preferred embodiment (cf FIG. 1, FIG. 2, FIG. 3, FIG.4, FIG. 7) that can be used as:

-   -   A bidirectional acceleration sensor or a bi-directional        seismometer    -   A bi-directional tiltmeter (inclinometer)    -   A gyroscope with the addition of an alternating voltage applied        on comb electrodes 20 and 21 (FIG. 11) instead of the plain        electrodes 4 (or 4′ and 4″).    -   A bidirectional actuator.    -   A gravimeter.

In the preferred embodiment described in FIG. 1, FIG. 2, FIG. 3, FIG. 4,and FIG. 7,

a diamagnetic disc 1 is surrounded with a cylindrical aluminum crown 3and is levitated over a Halbach-2D array 2 (cf. FIG. 13.f) of permanentmagnets 10.

The position of the disc 1 is controlled in a feed-back loop.

This feed-back loop is made of:

-   -   2 pairs of electrodes 11 made by the association of the aluminum        crown 3 and copper electrodes 4. The four electrostatic        actuators are diametrically disposed in pairs along two        orthogonal axis. One of the electrode of such actuators is the        cylindrical aluminum crown 3 and the other electrode of each        actuator, has a cylindrical shape as seen on FIG. 3, FIG. 7 and        FIG. 10.    -   a 4 segments optical sensor 5 spotted by an infrared LED 6-7-15        through the diamagnetic disc 1 and through 2.    -   and a digital controller 5 that generates the required voltages        (FIG. 2 and FIG. 3) to the 2 pairs of electrodes 11 (or 4+3) in        order to maintain (thanks to the generated electrostatic forces        13) the diamagnetic disc 1 at a predefined position when it is        subjected to motion (due to shaking in case of a seismic sensor,        or due to angular displacement in case of an X-Y tiltmeter, or        due to a variation of g in the case of a gravimeter).

In the case of, for instance, the seismometer application, the forces 13generated by the control 12 (or the voltages applied to the electrodes4) are proportional to the soil accelerations.

As we can see in FIG. 4 the measurements (X and Y) with the foursegments optical sensor 5 are differential.

The advantage of such a differential measurement is that it cancels outthe effect of temperature (or pressure or humidity . . . ) variations.

Of course we can also use 2 pairs of position sensors 16 (FIG. 10)(facing each others around the aluminum disc 1, cf FIG. 10) and we wouldalso have differential measurements: subtracting the output signal oftwo diametrically opposite sensors 16 gives the position information ofthe inertial mass 1+3 along the direction defined by the two saiddiametrically opposite sensors 16.

The sensors 16 are non-contact position sensors; they can be opticalreflection sensors, eddy current sensors, capacitive sensors (with acomb structure for instance) or interferometric sensors.

Of course, a signal-conditioning unit is needed for the non-contactposition sensor(s) 5 or 16 and also a high voltage power supply or ahigh voltage amplifier 14, with at least two inputs and four outputs, isneeded to apply high voltage (with very low currents) to the electrodes.

If a feedback loop along a direction Z, orthogonal to the X-Y plan ofthe magnet array, incorporating a Z electrostatic actuator, as well as,at least, one Z position sensor (facing one of the face of the inertialdisc), is added to the inertial sensing system embodiment describedpreviously, then the whole system becomes an X-Y-Z actuator and the highvoltage amplifier needs an additional input and an additional output.The Z actuator consists of at least one electrostatic actuator made ofthe diamagnetic disc 1 and the array of magnets 2 on which a highvoltage is applied in order to attract the diamagnetic disc.

Such an actuator can be used as the scanning module for an Atomic ForceMicroscope probe. The AFM probe is fixed in the centre of thediamagnetic disc 1 and points downward, towards the array of magnets 2.Just under the AFM probe, a magnet of the magnet array 2 has beenremoved from the magnet array 2 and the element to be scanned ispositioned inside the hole left by the missing magnet;

Such a triaxial actuator (X-Y-Z) can also be used as a precisepositioning unit that can, for instance, be incorporated in a larger X-Ytable.

The preferred arrangement for inertial sensing systems, or forbidirectional or tri-directional actuators, is a 2D (such as Halbach 2Dor opposite 2D) array of magnets in the configuration of FIG. 9.

Indeed, depending on both the shape of the inertial mass 1+3 and theshape of the 2D magnet array

FIG. 5, FIG. 6, FIG. 7, FIG. 8, FIG. 9, several kinds of stabilisationof the inertial mass can be achieved:

-   -   In FIG. 5 the diamagnetic material 17 has a rectangular shape        and is stably floating over a Halbach 1D. Such a configuration        is especially well adapted to design a linear diamagnetic drive        that can, for instance be used to convey small spare parts in a        microfactory.    -   In FIG. 6 the diamagnetic material 17 has a square shape and is        in a six degree of freedom stable and passive levitation over a        Halbach 2D array of permanent magnets. This configuration is        illustrated in FIG. 8.

In FIG. 7 the diamagnetic disc 1 with an aluminium crown 3 constitutesan unstable contact-less suspension which is radially stabilized withactive electrostatic actuators 3+4. This configuration corresponds tothe configuration illustrated in FIG. 9. Such a configuration is welladapted to the design of inertial sensing system as described in thepresent invention.

As for the 2D magnet array it does not have to be a Halbach 2D array (2or FIG. 13-f), it can be any of the possible magnets arrays shown inFIG. 13. The Halbach 2D array (2 or FIG. 13-f), is the one whichproduces the largest diamagnetic force among all those arrays; but, forinstance, an opposite 2D array FIG. 13-a of magnets can also be used andit is auto-stable (that is to say: no glue is needed for the assembly ofthis array) by opposition to the Halbach 2D array (2 or FIG. 13-f).

Except for the use of this inertial sensor as a gyroscope, the shape ofthe inertial mass 1+3 does not have to be a disc nor a cylinder; It canbe a parallelepiped, a triangle or a square for instance.

To be used as a gyroscope, some small changes have to be applied to thepreferred embodiment:

-   -   The aluminium crown 3 is replaced by an electret crown that can        be pre-charged or not.    -   The plain copper electrodes 4 are replaced by comb shaped        electrodes 20-21 with at least three phases as described in        FIG. 11. The inertial mass 1+3 rotates when a rotating electric        field is applied to such electrodes    -   Some additional plain electrodes 4′ (cf.FIG. 12), pointing        towards the inner surface of the electret crown can be added to        better stabilize the axial movements of the inertial mass.

Of course the place of the plain electrodes 4′ and the comb shapedelectrodes 20-21 can be inverted; that is to say the plain electrodes 4′(cf.FIG. 12), points towards the outer surface of the electret crown andthe comb shaped electrodes 20-21 point towards the inner surface of theelectret crown.

The electrodes 4 do not have to be made of copper but they should bemade of a non-ferromagnetic metal. Indeed, the electrodes 4 being placednext to the array of permanent magnets 2, the flux line 18 of the later2 would be severely modified if the electrodes 4 where made of aferromagnetic material. In addition, an insulation layer 8 is needed onelectrodes 4-4′-4″ or on the aluminum crown 3 in order to avoid shortcircuits when the inertial mass 3+1 is in contact with more than oneelectrode 4.

The number of electrostatic electrodes needed to conceive inertialsensing systems as described on this invention, could be reduced to 3;the control would be a little bit more complicated than with 4electrodes but the high voltage power supply stage would only need 3independent outputs whereas it needs 4 independent outputs in the 4electrodes embodiment.

Moreover the electrostatic force exerted on the inertial mass can bedoubled by using double electrodes as illustrated in FIG. 12. In such aconfiguration the voltage applied to an inner copper electrode 4″ is thesame as the voltage of the diametrically opposed outer electrode 4′.

As for the crown 3, it does not have to be made of aluminum, it can bemade of an electret (pre-charged or not) or a non-ferromagnetic metal.

Indeed, the crown 3 cannot be made of ferromagnetic metal because,otherwise, it would be attracted towards the magnet array and it wouldcancel the diamagnetic force as well as the diamagnetic levitation.

The main parameters of this inertial sensing system, such as theequivalent rigidity and damping of the electrostatic actuators, can bevaried by changing numerical values in the digital controller. Hence thebandwidth of the sensor is user selectable. In addition somepre-processing or processing tasks can be implemented directly in thedigital controller and the results can be saved in a data storagecomponent.

In addition with the adjunction of a compensating magnet a bigger bodycan be diamagnetically levitated and other apparatus such as flywheelcan be designed or larger inertial masses can be used for the inertialsensor of the present invention.

Everything that has been previously said about the inertial sensingsystem application can also be applied for the bi-directional X-Y andtri-directional X-Y-Z actuator.

The precision of the measurements will mainly depend on the electronicsused (resolution and sensitivity of the sensor, number of bits of the ADconverters, number of bits used in the controller, etc. . . . );

and if we apply the void inside the system, we can also enhance theprecision of the measurements.

1. Inertial sensor based on diamagnetic levitation, said inertial sensorcomprising a two dimensional array of permanent magnets and adiamagnetic element facing the said array characterized in that saiddiamagnetic material constitutes the inertial mass.
 2. Inertial sensoraccording to claim 1 wherein said array is a bi-dimensional arrangementof permanent magnets called “Halbach 2D” which is characterised by thefact that: some of its constituting magnets are pointing in a directionZ orthogonal to the XY plan defining said array the magnetic field linesare mostly concentrated on one side of the said array and with very fewmagnetic field lines on the other side of said array along each of thetwo directions X and Y defining said “Halbach 2D” array of permanentmagnets, one can see linear Halbach arrangements of permanent magnets:the polarities of adjacent magnets (along one direction) differ by anincrements of 90° in order to avoid breaking the symmetry of the fluxlines there are some missing magnets in the said array, and thosemissing magnets are located along directions parallel to the X+Ydirection of the said magnet and in between 2 magnets with the samevertical polarisation.
 3. Inertial sensor according to claim 1furthermore comprising a feed-back loop incorporating: at least 1 noncontact position sensor to detect the movements of said inertial mass atleast 3 electrostatic actuators for keeping in place or moving saidinertial mass and computing means to derive the solicitation exerted onsaid support means and for moving or keeping in place said inertial massaccordingly; wherein said electrostatic actuators have one commonelectrode which is physically sealed to said inertial mass, the otherelectrode of each said electrostatic actuator facing and partlysurrounding, or being partly surrounded by, said common electrode. 4.Inertial sensor according to claim 3 comprising two pairs of electrodesa 4 segments optical sensor a LED or laser source wherein said inertialmass is a disc of diamagnetic material surrounded by an aluminium crownthus constituting said common electrode; and wherein said pairs ofelectrodes are diametrically facing said aluminium crown, each said pairof electrodes being placed orthogonally to the other pair of electrodes;and wherein said 4 segments optical sensor and said LED or laser sourceare respectively facing an opposite face of the surface delimited bysaid inertial disc shaped mass; and wherein said inertial mass has ahole in its centre from which the light of said LED or laser source isspotting on said 4 segments optical sensor.
 5. Inertial sensor accordingto claim 3 comprising: two pairs of electrodes two pairs of non contactposition sensor wherein said inertial mass is a disc of diamagneticmaterial surrounded by an aluminium crown thus constituting said commonelectrode; and wherein said pairs of electrodes are diametrically facingsaid aluminium crown, each said pair of electrode being placedorthogonally to the other pair of electrode; wherein said pairs of noncontact position sensor are diametrically facing said aluminium crown,each said pair of electrode being placed orthogonaly to the other pairof electrode.
 6. Use of an inertial sensor according to claim 1 as abidirectional non-contact accelerometer or a bidirectional non contactseismometer.
 7. Use of an inertial sensor according to claim 1 as a noncontact bidirectional inclinometer or tiltmeter.
 8. Use of an inertialsensor according to claim 1 as a non contact gravimeter.
 9. Inertialsensor according to claim 3 wherein said inertial mass has a cylindricalshape; and wherein said electrostatic electrodes are positionedregularly spaced on the surface of a cylinder facing said commonelectrode of said electrostatic actuator; and wherein said commonelectrode of said electrostatic actuators is covered by a layer ofpre-charged electret and the other electrode of each of saidelectrostatic actuator is made of at least three independentelectrostatic alternating combs so as to create a rotating electricfield that can spin said inertial mass.
 10. Use of an inertial sensoraccording to claim 9 as non contact gyroscope.
 11. Bi-directionalactuator based on diamagnetic levitation, said bi-directional actuatorcomprising support means serving as main support body for abi-directional actuator, a two dimensional array of permanent magnetsand a diamagnetic material facing the said array characterized in thatsaid diamagnetic material constitutes the moving part of the actuator.12. Bi-directional actuator according to claim 11 wherein said array isa bi-dimensional arrangement of permanent magnets called “Halbach 2D”which is characterised by the fact that: some of its constitutingmagnets are pointing in a direction Z orthogonal to the XY plan definingsaid array the magnetic field lines are mostly concentrated on one sideof the said array and with very few magnetic field lines on the otherside of said array along each of the two directions X and Y definingsaid “Halbach 2D” array of permanent magnets, one can see linear Halbacharrangements of permanent magnets: the polarities of adjacent magnets(along one direction) differ by an increments of 90° in order to avoidbreaking the symmetry of the flux lines there are some missing magnetsin the said array, and those missing magnets are located alongdirections parallel to the X+Y direction of the said magnet and inbetween 2 magnets with the same vertical polarisation. 13.Bi-directional actuator according to claim 11 furthermore comprising afeed-back loop incorporating: at least 1 position sensor to detect themovements of said moving part of the actuator at least 3 electrostaticactuators for keeping in place or moving said moving part of theactuator and computing means to move or keep in place said moving partof the actuator; wherein said electrostatic actuators have one commonelectrode which is physically sealed to said inertial mass, the otherelectrode of each said electrostatic actuator facing and partlysurrounding, or being partly surrounded by, said common electrode. 14.Bi-directionnal actuator according to claim 13 comprising two pairs ofelectrodes a 4 segments optical sensor a LED or laser source whereinsaid inertial mass is a disc of diamagnetic material surrounded by analuminium crown thus constituting said common electrode; and whereinsaid pairs of electrodes are diametrically facing said aluminium crown,each said pair of electrode being placed orthogonaly to the other pairof electrode; and wherein said 4 segments optical sensor and said LED orlaser source are respectively facing an opposite face of the surfacedelimited by said inertial disc shaped mass; and wherein said inertialmass has a hole in its center from which the light of said LED or lasersource is spotting on said 4 segments optical sensor.
 15. Bi-directionalactuator according to claim 13 comprising: two pairs of electrodes twopairs of non contact position sensor wherein said inertial mass is adisc of diamagnetic material surrounded by an aluminium crown thusconstituting said common electrode; and wherein said pairs of electrodesare diametrically facing said aluminium crown, each said pair ofelectrodes being placed orthogonaly to the other pair of electrodes;wherein said pairs of non contact position sensor are diametricallyfacing said aluminium crown, each said pair of electrode being placedorthogonaly to the other pair of electrode.
 16. Bi-directional actuatoraccording to claim 13 comprising: at least two additional electrostaticelectrodes placed in such a way that said diamagnetic material is placedin between each of these two additional electrodes; said diamagneticmaterial playing the role of a common electrode in the 2 newelectrostatic actuators constituted by the association of saidadditional electrostatic electrodes and said diamagnetic material atleast an additional non contact position sensor to measure the positionof the said diamagnetic material with respect to said additionalelectrodes; wherein said diamagnetic element is a flat shapeddiamagnetic material; and wherein said position sensor is incorporatedin a feedback loop with said additional electrostatic actuators and saidcomputing means.
 17. Use of a Bi-directional actuator according to claim16 as a scanning module for an Atomic Force Microscope probe, said AFMprobe being fixed on said diamagnetic material facing said hole in said2D arrangement of permanent magnets; the element to be scanned beingpositioned inside said hole, under said AFM probe.